CPM Seminar

Shedding Light on Surface Reactions:
Real Time Imaging and Control of Pattern Formation during Catalysis

Harm Hinrich Rotermund

Department of of Physics and Atmospheric Science
Dalhousie University

Simple surface reactions like the CO-oxidation on single crystal Pt surfaces show a rich variety of pattern formation under specific reaction parameters. To visualize those patterns we have conceived several unique imaging methods starting around 1990. Part of the lecture will concentrate on those methods, and illustrate them with a variety of real time patterns [1].

The interaction of a multitude of micrometer scale concentration waves and fronts on the surface complicate our understanding the underlying mechanisms for such patterns. Experiments with modified catalytic activity using stationary, inactive boundaries have therefore been designed to isolate individual features (for example single pulses) and interaction mechanisms in order to study them quantitatively [2]. Since 2001 we have been able to dynamically change the surface catalytic activity in real time and space by focusing an addressable laser beam to differentially heat a Pt(110) single crystal surface [3].

Imaging the reactants local coverage with an ellipso-microscope enabled us to close the loop between sensing and actuation, both being spatial-temporally resolved. Pulses and fronts, the basic building blocks of patterns, can now be formed, accelerated, modified, guided and destroyed at will. A temperature heterogeneity moving along a line may ignite waves along its path, or can drag preexisting pulses.

The combination between the fixed microstructures of metals with different catalytic activities and local laser heating of the surface has been recently explored and will be discussed [4].

[1] H. Rotermund, Surf. Sci. Rep. 29, 265-364 (1997).
[2] M. Pollmann, H. Rotermund, G. Ertl, X. Li, G. Kevrekidis, Phys. Rev. Lett. 86, 6038-41 (2001).
[3] J. Wolff, G. Papathanasiou, G. Kevrekidis, H. Rotermund, G. Ertl, Science 294, 134-7 (2001).
[4] C. Punckt, S. Merkt, H. Rotermund, New Journal of Physics 9, 213-228 (2007).